From: "Xiang Mei (Microsoft)" nft_payload_offload_mask() builds the offload match mask for a payload expression that covers only part of a header field. For a partial IPv6 address match (field_len = 16, priv_len = 1) that shift is 1 << 120, which is undefined on the 32-bit int operand. It also trims only one word, so the remaining words stay 0xffffffff (and when priv_len is a multiple of 4 the trim is skipped entirely), leaving the mask covering more bytes than the rule matches. UBSAN: shift-out-of-bounds in net/netfilter/nft_payload.c:278:20 shift exponent 120 is too large for 32-bit type 'int' ... The match is byte-granular and struct nft_data is zero-initialised, so the correct mask is simply the first priv_len bytes set to 0xff. Set those bytes directly and drop the word/shift trimming; this removes the undefined shift and no longer over-masks the trailing bytes. Fixes: a5d45bc0dc50 ("netfilter: nftables_offload: build mask based from the matching bytes") Reported-by: AutonomousCodeSecurity@microsoft.com Signed-off-by: Xiang Mei (Microsoft) Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nft_payload.c | 12 +----------- 1 file changed, 1 insertion(+), 11 deletions(-) diff --git a/net/netfilter/nft_payload.c b/net/netfilter/nft_payload.c index 391539a1ceaa..8a4472fd77d9 100644 --- a/net/netfilter/nft_payload.c +++ b/net/netfilter/nft_payload.c @@ -259,9 +259,7 @@ static int nft_payload_dump(struct sk_buff *skb, static bool nft_payload_offload_mask(struct nft_offload_reg *reg, u32 priv_len, u32 field_len) { - unsigned int remainder, delta, k; struct nft_data mask = {}; - __be32 remainder_mask; if (priv_len == field_len) { memset(®->mask, 0xff, priv_len); @@ -270,15 +268,7 @@ static bool nft_payload_offload_mask(struct nft_offload_reg *reg, return false; } - memset(&mask, 0xff, field_len); - remainder = priv_len % sizeof(u32); - if (remainder) { - k = priv_len / sizeof(u32); - delta = field_len - priv_len; - remainder_mask = htonl(~((1 << (delta * BITS_PER_BYTE)) - 1)); - mask.data[k] = (__force u32)remainder_mask; - } - + memset(&mask, 0xff, priv_len); memcpy(®->mask, &mask, field_len); return true; -- 2.47.3